1. Field of the Invention
The present invention relates to a driving device for selectively moving a plurality of driven members from the position on one and the same axis to a predetermined position by switching the use of the driven members from one over to another, or a filter change-over device for change-over of ND (neutral density) filters or the like to be used by being inserted into and retracted out of an optical path for adjustment of light quantity in an image pickup device of an optical apparatus, such as a video camera or the like, and more particularly to a filter change-over device arranged to selectively insert a plurality of filters of different densities into the optical path by changing use of them from one over to another.
2. Description of Related Art
Zoom lenses for video cameras have been most popularly composed of four lens units, i.e., in order from the object side, a positive fixed lens unit, a negative movable lens unit, a positive fixed lens unit and a positive movable lens unit. The known zoom lenses adapted for video cameras of course include other zoom lenses arranged differently from the lens arrangement mentioned above.
FIGS. 12(A) and 12(B) show the construction of a zoom lens barrel of the most popular four-lens-unit arrangement. As shown in FIGS. 12(A) and 12(B), the zoom lens is composed of four lens units 201a to 201d, i.e., a front lens unit 201a which is fixed, a variator lens unit 201b which is arranged to perform a magnification varying action by moving along an optical axis 205, an a focal lens unit 201c which is fixed, and a focusing lens unit 201d which is arranged to move along the optical axis 205 to keep a focal plane constant when the magnification varying action is performed as well as to adjust focus.
Referring to FIGS. 12(A) and 12(B), guide bars 203, 204a and 204b are arranged in parallel with the optical axis 205 to guide the moving lens units and also to prevent the moving lens units from rotating. A DC motor 206 is a drive source arranged to move the variator lens unit 201b. While the DC motor 206 is used as the drive source for the variator lens unit 201b, a stepping motor may be used in place of the DC motor 206, in the same manner as a stepping motor which is used as a drive source for the focusing lens unit 201d. 
The variator lens unit 201b is held by a holding frame 211. The holding frame 211 is provided with a pressing spring 209 and a ball 210 which is pushed by the force of the pressing spring 209 to engage a screw groove 208a formed in a screw bar 208. Therefore, when the screw bar 208 is driven to rotate by the DC motor 206 through an output shaft 206a and a gear train 207, the holding frame 211 moves in the direction of the optical axis along the guide bar 203.
The focusing lens unit 201d is held by a holding frame 214. The holding frame 214 has a sleeve part fitted on the guide bar 204b to act as a guide. A screw member 213 is arranged in the neighborhood of the sleeve part to be in one body with the holding frame 214 in the direction of the optical axis. When a stepping motor 212 is caused to rotate, its output shaft 212a rotates. Then, a male screw part formed on the output shaft 212a and a female screw part or a rack part formed in the screw member 213 move in association with the rotation of the stepping motor 212. This causes the holding frame 214 to move in the direction of the optical axis along the guide bars 204a and 204b. The details of a part where the holding member 214 and the screw member 213 are coupled with each other are disclosed, for example, in Japanese Laid-Open Patent Application No. HEI 4-136806.
As mentioned above, the interlocking mechanism of the stepping motor 212 is applicable also for driving the variator lens unit 201b. 
In a case where a lens unit is arranged to be moved by a stepping motor together with a moving frame, as described above, the absolute position in the direction of an optical axis of the lens unit can be detected by arranging a photo-interrupter (not shown) and a light-blocking wall which is formed integrally with the moving frame and by arranging one reference position of the moving frame in the direction of the optical axis to be detectable with the photo-interrupter and the light-blocking wall. Position detecting means can be thus arranged to be capable of detecting the absolute position of a lens holding frame, i.e., the moving frame, by setting the lens holding frame at the reference position and, after that, by continuously counting the number of driving pulses applied to the stepping motor.
FIG. 13 is a block diagram showing the electrical arrangement of a camera body included in a conventional image pickup apparatus. In FIG. 13, all parts that are indicated by the same reference numerals as in FIGS. 12(A) and 12(B) are arranged in the same manner as those shown in FIGS. 12(A) and 12(B).
Referring to FIG. 13, a solid-state image sensor 221 is composed of a CCD, etc. A zoom drive source 222 is arranged to drive the variator lens unit 201b. The zoom drive source 222 includes the motor 206, the gear train 207 which is interlocked with the motor 206, the screw bar 208, etc. The zoom drive source 222 may be also arranged to include a stepping motor, etc., in the same manner as the focusing lens unit driving arrangement shown in FIG. 12(B). A focusing drive source 223 is arranged to drive the focusing lens unit 201d and includes the stepping motor 212, the output shaft 212a which has a male screw formed thereon and the screw member 213 which is arranged integrally with the holding frame 214 in the direction of the optical axis.
The camera body further includes a diaphragm drive source 224, a zoom encoder 225 and a focus encoder 227. The zoom and focus encoders 225 and 227 are arranged to respectively detect the absolute positions of the variator lens unit 201b and the focusing lens unit 201d in the direction of the optical axis. In a case where a DC motor is employed as the drive source for driving the variator lens unit 201b as in the case of FIG. 12(A), an absolute position encoder such as a potentiometer or the like is employed as the zoom encoder 225. A magnetic encoder may be used instead of using a potentiometer.
In a case where a stepping motor is employed as a drive source, the absolute position of a lens unit is generally detected by setting a lens holding frame at a reference position and by continuously counting the number of operating (driving) pulses applied to the stepping motor, as mentioned above.
A diaphragm encoder 226 is arranged by having a Hall element inside of a meter which is a drive source for a diaphragm 235 and by detecting a relation between the rotating position of a rotor and that of a stator.
A camera signal processing circuit 228 is arranged to perform an amplifying process, a gamma correction process, etc., on a video signal outputted from a CCD 221 in a predetermined manner. A contrast signal of the video signal thus processed passes through an AE gate 229 and an AF gate 230. These gates 229 and 230 are arranged to set and determine an optimum signal fetching range within the whole image plane for determining an exposure and for focus adjustment. Such a gate either may be arranged to have a variable size or may be plurally arranged. However, for the sake of simplification of description, the details of the gate arrangement are omitted from the description.
An AF signal processing circuit 231 is provided for automatic focusing (AF) and is arranged to form one or a plurality of outputs relative to high-frequency components of a video signal. A zoom switch 233 is connected to a CPU 232. A zoom tracking memory 234 is arranged to store information on focusing lens positions to be taken according to object distances and variator lens positions obtained when a magnification varying action is performed. A memory disposed within the CPU 232 may be used as the zoom tracking memory 234.
When the zoom switch 233 is operated by the user of the apparatus, for example, the CPU 232 acts to keep the variator lens unit 201b and the focusing lens unit 201d in a predetermined positional relation computed on the basis of information stored in the zoom tracking memory 234. For this purpose, the CPU 232 drives and controls the zoom drive source 222 and the focusing drive source 223 in such a way as to cause the current absolute position of the variator lens unit 201b in the direction of the optical axis as detected by the zoom encoder 225 to coincide with a computed position of the variator lens unit 201b and also to cause the absolute position of the focusing lens unit 201d in the direction of the optical axis as detected by the focus encoder 227 to coincide with a computed position of the focusing lens unit 201d. 
In the automatic focusing action, the CPU 232 drives and controls the focusing drive source 223 in such a way as to make the output of the AF signal processing circuit 231 have a peak thereof.
Further, in order to obtain an apposite exposure, the CPU 232 acts to have the average value of the output of a luminance signal passing through the AE gate 229 at a predetermined value by controlling the diaphragm drive source 224 to cause the aperture diameter of the diaphragm 235 to be at a position where the output of the diaphragm encoder 226 becomes the predetermined value.
When the aperture is stopped down to an aperture diameter smaller than a predetermined value, an image on an image forming plane is caused to deteriorate by the diffraction of light. This phenomenon is well known. If the object of shooting is located under a bright outdoor condition, in controlling the aperture of the diaphragm to make the average value of a luminance signal outputted as a contrast signal from the image sensor which is a CCD or the like, the diaphragm aperture would become smaller than an aperture diameter at which such a diffraction of light takes place. The quality of an image picked up under such a condition, therefore, tends to deteriorate.
To solve this problem, video cameras adapted for general users are arranged as follows. An ND filter is stuck to the blades of the diaphragm to be in one body therewith to prevent occurrence of diffraction at a small aperture by gradually covering the aperture with the ND filter accordingly as the aperture is stopped down to a smaller diameter. If the object of shooting is very bright and the small-aperture diffraction still takes place despite of this arrangement, the shutter speed (electric charge take-in time in the case of a CCD) of the video camera is arranged to become faster so that an exposure can be made in an optimum manner.
However, if the ND filter of the light quantity adjustment system is arranged to cover the aperture in an intermediate position with respect to the aperture, either a luminescent spot uncleanly blurs at distances before and after a main object of shooting or the quantity of light obtained within an image plane becomes uneven.
It has been known to solve these problems by inserting the ND filter into an optical path in a retractable state separately from the diaphragm, instead of sticking the ND filter to the diaphragm blades.
For this purpose, a filter change-over device is mechanically arranged as a driving device to selectively move a driven member (the filter) to a predetermined position. FIG. 14 shows one example of such a filter change-over device as viewed in the direction of the optical axis.
Referring to FIG. 14, an ND filter part 256 is made of a resin film or the like. A filter frame 252 is illustrated by a full line in a state of being within the optical path and by a broken line in a state of being outside of the optical path. Fixing claw parts 257 are arranged to secure the ND filter part 256 to the filter frame 252. Reference numeral 253 denotes the center of rotation of the filter frame 252. The filter frame 252 is provided with a boss part which is formed integrally with one end part of the filter frame 252. An operation switch 251 is illustrated by a full line as it is in a state of having the ND filter part 256 within the optical path and by a broken line as it is in a state of having the ND filter part 256 outside of the optical path. The operation switch 251 is arranged, for example, on an external side part of the lens barrel to be operated in the direction of an arrow 254. A tension spring 258 is arranged to pull the filter frame 252 toward the outside of the optical path.
When the operation switch 251 which is on the outside of the lens barrel is vertically slid by the user, the boss part 260 which is interlocked with the operation switch 251 causes the filter frame 252 to rotate around the rotation center 253 to change the position of the ND filter part 256 between its positions inside and outside of the optical path, from one position over to the other.
In a case where it is insufficient to set only one kind of the ND filter, some of known lens barrels have been arranged to have a plurality of filters coaxially arranged side by side in a turret-type structure to have one center of rotation and to be selected one after another. Further, in such a case, some filters that give special effects are sometimes used in place of the ND filters.
However, the turret-type filter change-over device necessitates arrangement of a rotary disk having filters mounted thereon, which sometimes has hindered efforts to make lens barrels in small size.
The invention is directed to the reduction in size of a driving device for selectively moving a plurality of driven members to a predetermined position and in size of a filter change-over device and an optical apparatus.
To attain the above object, in accordance with an aspect of the invention, there is provided a filter driving device, which comprises a first optical filter member, a second optical filter member, and rotary driving means, the rotary driving means being operable to be rotated in a predetermined rotating direction so as to drive the first and second optical filter members to selectively bring about one of a state in which the first optical filter member is located on an optical path, a state in which the second optical filter member is located on the optical path and a state in which neither of the first and second optical filter members is located on the optical path.
In particular, in the above-stated filter driving device, the rotary driving means is an operation lever operable to be rotated around a predetermined axis.
Further, in the filter driving device, the rotary driving means is arranged to be rotated by a motor.
Further, in the filter driving device, the first and second optical filter members are arranged to rotate around a common axis of rotation.
Further, in the filter driving device, each of the first and second optical filter members is a neutral density filter.
In addition, the filter driving device further comprises an urging member arranged to exert urging forces on the first and second optical filter members to urge the first and second optical filter members respectively to rotate in opposite directions around the common axis of rotation. The rotary driving means is a lever member. The lever member is arranged to rotate around an axis of rotation different from the common axis of rotation so as to drive the first and second optical filter members.
In the above-stated filter driving device, the lever member is provided with abutting parts arranged to abut on the first and second optical filter members.
In addition, in the filter driving device, the rotary driving means includes a rotary member arranged to rotate around an axis of rotation different from the common axis of rotation, a first cam member arranged to drive the first optical filter member by rotating integrally with the rotary member around the axis of rotation of the rotary member, and a second cam member arranged to drive the second optical filter member by rotating integrally with the rotary member on the axis of rotation of the rotary member.
Further, in the above-stated filter driving device, the rotary member is provided with a gear which is formed along a periphery thereof and is coupled with an output gear of a motor.
Further, in the filter driving device, the rotary driving means is arranged to drive the first and second optical filter members so as to bring about a further state in which both the first and second optical filter members are located on the optical path.